The subtitle says it all: "The American Tribal Love-Rock Musical." These words describe Hair with such precision, that just to see them is to imagine the tangled manes, open love, and billowing clouds of fragrant marijuana smoke that will forever identify the 1960s. Is there anything that more successfully summons the shimmering vivacity of the decade?

Certainly not. But is that a good thing?

No appraisal of the Galt MacDermot-James Rado-Gerome Ragni musical, or of the spirited but dispiriting Public Theater revival of it that just opened at the Delacorte Theater in Central Park, is possible without considering the circumstances that the work's very nature demands surround it. And if examined only on the most elemental level, Hair is innovative, tuneful, and as warmly breezy as an August night.

Unfortunately, this musical demands a more probing look, one which reveals a show that can never be taken strictly on its own terms. The Public production, which has been directed by Diane Paulus and choreographed by Karole Armitage to burst with adolescent ardor, reveals a show at once timeless and dated.

It continues to persist and tease primarily because of its score, which is crammed with contemporary classics. It's rare that a show begins with a number as undulatingly persuasive as the invocational "Aquarius" and has nowhere to go but up. But MacDermot's music and Gerome Ragni and James Rado's lyrics (they also did the book) consistently challenge and improve upon themselves. "Manchester, England," "Easy to Be Hard," "Frank Mills," "Black Boys" and "White Boys," "Good Morning Starshine," "Let the Sun Shine In," and of course the title song burst with the devil-may-care, rebellious whimsy that typifies a musical convinced it has nothing to lose.

Then there's the structure, which remains formless and fascinating. This story of high-school social discontent, as represented by Claude (Jonathan Groff), Berger (Will Swenson), and their just-drafted friends and girlfriends, is thrust through the solidified-mirage concept of a living protest circle. As everyone cavorts, carouses, and challenges prevailing wisdoms with their new outlook, scenes, speeches, and songs don't merely emerge, but are yanked from the air in real time. All lines between what is in the theatre, what is outside the theatre, and what could be are obliterated.

At least ideally. And perhaps when Hair first opened, either Off-Broadway in 1967 or on Broadway the following year. But less so now. This is because of that simplest and cruelest of reasons: the passage of time. In his curtain speech at the performance I attended, Public Theater Artistic Director Oskar Eustis said of founder Joseph Papp's vision for the musical: "It wasn't enough to take the canon and offer it up for free to the people, to really complete the democratic circle you had to take the voice of the people and make it part of the canon." Is Hair still the voice of the people?

With no more draft, no more Lyndon Johnson to rail against, and no more hippies (at least of any notable influence), one can mine topicality only from the show's fervent antiwar bent - always but one portion of a work of far greater scope. So too has the theatre itself eclipsed the people it once simply chronicled: Critical illusions are spoiled by Scott Pask's use of Astroturf in extending Central Park onto the Delacorte stage, and by the performers who flaunt body mics and generally look like they'd be more willing to die in Vietnam than to burn their gym membership cards.

Tommar Wilson, Will Swensen, and Bryce Ryness.Photo by Michal Daniel.

The present can't assault the past so ruthlessly and maintain authenticity; for all its affected shagginess (most notably in Michael McDonald's costumes) this production is more creamily nostalgic than grittily real. The performers all sound terrific, but the few who stand out - Groff, bearing just the right air of disaffection; Caren Lyn Manuel as the forever-scorned Sheila (who sings the pointed "Easy to Be Hard"); Patina Renea Miller as the "Aquarius" soloist - do so because they leap most successfully across the generational barrier. Most of the other actors (especially the seething Swenson) are at best approximating; Paulus and Armitage do little to discourage them.

It can't be easy for them - what was practically yesterday's news by 1968 is now even quainter, a yellowed newspaper that crumbles at the touch despite its exciting headlines. When young people today go to theatre, its malaise-tinged voice is echoed most closely in Spring Awakening, In the Heights, and Passing Strange. The type of kids Hair captured likely never yearned for the music of 40 years prior; one doesn't suppose Whoopee!, Chee-Chee, or The New Moon were cherished or relevant to them.

It's squarely at them, and no one else, that this production is aimed, which makes it more relic than revelation. The problems of growing up and growing into yourself are perennials, but require more decisive writing to escape being superglued to the ethos of its era. This deliciously shameless embodiment of free-spirited fun has always been spiked with sobriety, but it can't bear the weight of looking back rather than forward. Why should Hair stay mired in place, when its tribe has long since moved on?

Hair: The American Tribal Love-Rock Musical
Shakespeare in the ParkThrough August 31
Delacorte Theater in Central Park, Enter Central Park at 81st Street and Central Park West or 70th Street and Fifth Avenue.
This year, free tickets to Shakespeare in the Park will only be distributed at the Delacorte Theater in Central Park or via a new virtual line opportunity at www.publictheater.org. The Public Theater will not be distributing tickets downtown at 425 Lafayette Street due to ongoing construction on the exterior of the building.
Performances: Tuesday through Sunday at 8 pm